Guess the year and the place: “Jews kill babies” graffiti appears on the streets. Protesters wave their arms in a Hitler salute. Thugs surrounding a reporter and demanding “Are you a Jew?”, then telling him that if he is, “you’re not welcome here.” Otherwise unremarkable members of the public express support for genocide and gas chambers. The flags of totalitarian movements are erected in public places.

All these events could be comfortably identified as taking place eighty years ago, in Germany – a horror, but a historical horror, fading from living memory, studied enough to be stored securely on a musty library shelf and part of a world sufficiently alien and brutal that it appears distant. But, far more disturbingly, all actually took place within the last week, here in the UK (the various accounts are here, here, here, here and here).

These aren’t grainy black and white images from Munich or Berlin, they are going on right now on Oxford Street, in Kensington, on London council estates and in Manchester’s city centre. These events can’t be put in a case behind glass, or endlessly rehashed on the History Channel, they’re echoing outside Costa Coffee and Primark and creeping their way across Facebook and Twitter.

As one of the victorious powers in 1945, we have a well-developed, oft-repeated response to the anti-semitism of the Nazis. It was loathsome, founded on bigotry and pseudo-science, and thank goodness we helped to put a stop to it. “Never again,” we intone seriously, while wondering at the naivety and weakness of the appeasers of the 1930s.

And yet, we are barely more active in combating anti-semitism today than those who turned a blind eye to it eighty years ago. Several times in the last few days I’ve called out some of these racists on Twitter – including one particularly stupid example – and all too often the reply from others is that such hatred is to be expected given events in Gaza; or that when the person wrote “Jews”, they really meant “Zionists” (implicit but accidental proof that the substitution works the other way round, too); or that I’m a shill trying to distract from the actions of the Israeli military.

This is the verbal shield covering the return of one of Europe’s oldest evils.

Disturbingly, despite their shocking nature events in this country are relatively mild when compared to some of our neighbours. Even before the recent conflict in the Middle East, London synagogues saw an influx of French Jews crossing the Channel to escape an increasingly poisonous environment – a trend that can only have been accelerated by the smashing of Parisian shops and attacks on synagogues. In Germany, students report being assaulted purely for wearing a skullcap, while in Holland a mob at a pro-Palestinian rally chanted “Hamas! Hamas! Jews to the gas!”

Natan Sharansky is hopefully mistaken in saying, “I believe we are seeing the end of Jewish history in Europe”, but the diaspora is certainly shaken and increasingly considering its options. As Milo Yiannopoulos put it, “people aren’t exactly sleeping with packed suitcases under the bed – yet. But there’s a melancholic inevitability about the way Jewish people are quietly Googling flight prices”.

How has it come to this?

With a bitter irony, at least part of the answer lies in an excess, and abuse, of tolerance. The just struggle against racism gave birth to a perverse child: the development of multi-culturalism as a system of total tolerance, including the toleration of creeds which preach hatred and extermination. Islamists have become masters of playing the systems and sensitivites of modern society for all that they are worth.

A rejection of extremism will all too often be denounced as racist or islamophobic – arrogantly assuming, as such extremists do, that their own “pure” Islamism is the defining representation of Islam as a faith and a criticism of its proponents is an attack on Muslims as a group. In reality, this hateful rump is totally unrepresentative – but it has secured a voice far louder than is justified by its numbers.

Uninformed as to the realities of the situation, numerous well-intentioned people have fallen for the con. Others, nervous of seeming discriminatory – or of falling foul of the mercurial mobs who police supposed tolerance – have kept quiet even though they suspect and feel in their heart that something is very wrong.

At the same time, while anti-semitism has become less pronounced on the far right (often succeeded by bandwagon-jumping islamophobia), large tracts of the fashionable left allow it to grow within the Palestine solidarity movement. Atheist, gay rights-supporting left-wingers have come to loathe Israel so much that they seem not to think twice about marching alongside people whose ideal society would see them and the liberties they espouse exterminated.

Even worse, growing numbers have accepted the elision of the Israeli government and the Jewish people – last week, for example, the Cambridge Palestine Forum, which includes some of the most intelligent undergraduates in the land, tried to protest about Gaza outside the local synagogue. It was called off, happily, but trendy young activists who view themselves as humanitarian, politically correct advocates of social justice were planning a fundamentally racist event, apparently without a second thought.

The modern resurgence of anti-semitism has taken full advantage of legitimate concerns – about Palestinians’ rights, about IDF tactics, about the suffering of civilians used by Hamas as human shields – and used them to squirm its way back onto our streets, around the dinner table and into public conversation. We should never have allowed it to get this far; now it has, we must stop it in its tracks. If we don’t, “Never again” will seem like a sick joke.